With the recent exploitation of the utility of halogen-containing resin articles, halogen-containing resin articles for outdoor use have increased. In particular, articles for long-term outdoor use, such as pipes, deck materials, roofing materials, and siding materials (clapboards made of halogenated resins), undergo influences of heat and ultraviolet ray ascribed to sunlight or influences of rainwater and oxygen in air, and decrease in mechanical strength and change in appearance. The change in appearance is exhibited as a chalking phenomenon in which a part exposed to sunlight becomes whitened. When this phenomenon occurs, colors such as brown, blue, red and green applied to the articles during molding discolor to a whitish tint, and with time, the entire surface of the articles is whitened, and their merchandise value is markedly impaired.
The following explanations have been made so far to account for the chalking phenomenon. One is that in the surface layer of the article, the halogen-containing resin undergoes decomposition by light, and consequently, the coloring agent used becomes easy to extract and flows away with rainwater. The other is that since higher fatty acids or their metal salts as components of a heat stabilizer, a lubricant, etc. added at the time of processing and also a filler have poor compatibility with the halogen-containing resin, they migrate to the surface of the article.
Various ultraviolet absorbers have been used as a weatherability improver for halogen-containing resins. Some of them are effective for improving the properties of the halogen-containing resins, for example, for retaining their mechanical strength, but none have proved to be entirely satisfactory for the prevention of the chalking phenomenon of the halogen-containing resins.
One of the inventors of the present application discloses in Japanese Patent Publication No. 8051/1985 a chalking-free halogenated resin composition comprising 100 parts by weight of a halogenated resin and 0.01 to 5 parts by weight of at least one of copper oxide, copper hydroxide, copper halides and inorganic acid salts of copper.